Process for the hot forming of metal



R. c. M MASTER 3,534,574

PROCESS FOR THE HOT FORMING OF METAL Oct. 20, 1970 2 Shets-Sheet l Filed March 14, 1968 m AZ- v INVENTOR, ROBERT C; MCMASTER ATTORNEY United States Patent US. CI. 72-57 22 Claims ABSTRACT OF THE DISCLOSURE This invention is a process and system for the hot rolling and deformation of metallic materials in which sonic vibratory power is used to control the heating of metals and alloys prior to hot deformation.

CROSS REFERENCES There is disclosed in patent application, Ser. No. 571,490, for Electromechanical Transducer by Hildegard M. Minchenko, now US. Pat. No. 3,396,285, a transducer capable of delivering extremely high power, i.e., measurable in horsepower (or kilowatts) at an acoustical frequency range. The principle underlying the high power output is in the structural arrangement of the components immediately associated with the piezoelectric driving elements. In theory and practice, the piezoelectric driving elements are under radial and axial pressure that assure that they do not operate in tension even under intense sonic action. Significantly, the structural design of this transducer, that permits the extraordinary power output from the driving elements, resides in the novel method of clamping the piezoelectric elements both radially and longitudinally (axially). In this way the acoustic stresses in the piezoelectric elements are always compressive, never tensile, even under maximum voltage excitation.

The transducer disclosed in the aforementioned patent application is intended, and therefore utilized, to deliver a steady state vibrational power output. That is the piezo electric assembly is a component of a resonant structure that will produce a mechanical vibratory output at the frequency of the driving electrical signal and vice versa.

In the copending patent application, filed herewith, S.N., 713,036, filed Mar. 14, 1968, for Cold Working of Metals with Sonic Energy by Robert C. McMaster, vibratory energy is applied directly to the work material and need not vibrate any elements of the forming machinery at all. Very high vibratory stress levels (approaching the elastic limit of the work material) can be applied effectively by this process, without any limitations related to the ability of the processing machinery to withstand vibratory forces or accelerations. Cold rolling and forming systems of the copending application substitute dynamic force from a sonic motor for a very large portion of the static forces required. The vibratory energy from the transducer produces dynamic stresses which approach the elastic limit of the material but do not exceed it. The static force applied by the rolls causes the elastic limit to be exceeded and the material to deform. In conventional processes, metallic materials are deformed by static forces producing static stresses exceeding the elastic limits of the work materials. In this new system the role of the static force system is reduced to that of a control-signal system, the basic work of deformation being done by the dynamic vibrational stress waves caused by one or more sonic power transducers.

BACKGROUND AND PRIOR ART In the sonic and ultrasonic metal deformation systems disclosed in the prior art, sonic and ultrasonic vibrations ICC are introduced through the rolls, dies, press elements, mandrels, pierces and other elements commonly used for application of static forces and pressures to the surface of the work materials. In general, such systems were not effective for purposes other than some reduction in friction at the interface with the work material. The effort to vibrate the masses of rolls, dies, and other force application elements required extremely high vibratory forces to overcome the inertial forces (f=ma) of these elements. Very high levels of sonic power cannot be introduced into work materials by this means since the vibration lifts the forming element out of contact with the Work material unless very high static forces (exceeding the magnitude of the vibratory force) are superimposed. The latter condition eliminates the minor advantages of reduction of friction. Tools, dies, rolls, and other force application elements of this type tend to fail rapidly in fatigue. Where longitudinal deformation is desired benefits of applying vibratory force longitudinally to the work material are lost where the vibratory force is applied transversely to the work material through the rolls, dies, etc.

The prior art systems for hot forming metals require the metals to be preheated using preheating furnaces which are often large and costly. Before a metal is hot worked, it is heated to a temperature in the desired range in a furnace, removed from the furnace, transported to the working area and run through the working machinery. All the while the material is cooling, creating thermal gradients; the colder the metal, the higher the forces required to produce the desired deformation.

SUMMARY OF INVENTION In the present invention the vibratory energy is applied directly to the work material, and need not vibrate any elements of the forming machinery at all. Very high vibratory stress levels (approaching the elastic limit of the work material) can be applied effectively by this process, without any limitations related to the ability of the processing machinery to withstand vibratory forces or accelerations.

The hot forming method of the present invention differs radically from the prior art. The material is heated at a chosen position by flame or induction to initiate the process of the present invention. Prior to the heating, the sinusoidal stress level is near the elastic limit; upon heating, the elastic limit of the material is lowered in the heated area. The sinusoidal or fully reversed stress then exceeds the elastic limit, releasing heat by mechanical hysteresis, thereby enabling the temperature of the material to be regulated without further assistance by flame or induction. Further, this method substitutes dynamic force from a sonic motor producing high-amplitude vibratory stresses for a very large portion of the static forces required in all conventional present methods where metallic materials are hot-formed using static forces exceeding the elastic limits of the work materials. The role of the static force method is reduced to that of a controlsignal system, and the basic deformation is done by means of the dynamic vibrational stress waves caused by one or more sonic power transducers. In consequence, it is estimated that the static force requirements could be reduced in ratios of 10:1 to :1 or more, as compared with conventional static hot-forming systems.

OBJECTS The present invention has as its principal object a method for hot forming steels, aluminum alloys, titanium alloys, and all other materials possessing a stress-strain curve with an elastic region followed by a region of plastic deformation.

Another object of the invention is to provide a method of hot forming by which the hot forming may be completed in one continuous Operation eliminating the necessity for preheating and/or reheating.

Another object of the invention is to provide a method to change sonic energy introduced into a non-resonant metal into heat.

Another object of the invention is to provide a method to fix the location of the heated zone in the material at a given distance from the forming apparatus.

Another object of the invention is to provide a method to generate heat uniformly across the cross-section of the material eliminating thermal gradients between the surface and center.

Another object of the invention is to provide a method to maintain the temperature of the material at the optimum value.

Another object of the invention is to provide a method which will heat the metal to be hot worked with greater efficiency.

Another object is to provide a method which will reduce or eliminate the need for preheat facilities.

A further object of the invention is to reduce the weight, size, and cost of machinery required to perform a given hot forming operation.

Still another object of the invention is to increase the capabilities of existing hot forming machinery by ratios of :1 to 100:1 or more.

Other objects and features of the present invention will become apparent from a reading of the following detailed description when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a system for hot rolling materials using sonic power as a means for producing heat, reducing the static forces required to deform the material, and as a means of controlling the rate of cooling of the work material;

FIG. 2a is a graphical illustration of the different modes of sonic power and how the sonic power changes from one mode to another;

FIG. 2b is a graphical illustration of the elastic range of a typical stress-strain curve; viewed in conjunction with Mode I of FIG. 2a, observe that sonic vibratory energy which creates stress below the elastic limit is transmitted through the material with virtually no energy loss;

FIG. 2c is a graphical illustration of cyclic stressing beyond the elastic limit inducing power losses, the energy of which is manifested in the forms of mechanical hysteresis heating. This is Mode II;

FIG. 2a is a graphical illustration of the operation of Mode III when a static bias force is applied to the material which permits the tension and/or compression deformation of the material;

FIG. 3 is an example curve showing the variation of the elastic limit of a typical metallic material as a functron of temperature; and,

FIG. 4 is a graphical illustration of static force as a control-signal with constant-magnitude of vibratory stress.

DETAILED DESORIPTIO'N OF INVENTION Refer generally to FIGS. 1 and 2a. In the hot forming method concepts herein described, three modes of action of vibratory waves within the work material 2 are employed selectively, to obtain multiple benefits in processing. The description of these modes includes referring to segments I, II, and III of FIGS. 1 and 2a respectively:

Mode I.-Eflicient Transmission of Sonic Power in yetals, with maximum stress levels below the elastic lmit.

Mode II.Efiicient Conversion of Sonic Power into fIeat, with maximum stress levels exceeding the elastic imit.

Mode III.Substitution of Sonic Vibratory Force for Static Force, producing deformation with greatly reduced magnitudes of static force F required from rolls, dies, or other deformation tools. In this invention, hot rolling or hot forming with sonic power, each of these modes of response is utilized at selected points to aid the hot deformation processing of metals and alloys.

The location of the conversion of sonic energy into heat by Mode II mechanisms is established either (a) by preheating the material 2 in this zone by external means, such as flame or induction heating, for example, so as to lower the elastic limit of the material below the peak vibratory stress, or (b) by reducing the work material 2 cross-section so as to increase the peak vibratory stress 8 level so it exceeds the elastic limit 6, 7 of the work material 2.

A unique advantage of the present invention over prior art is that the temperature of the entire cross-section is uniformly raised to and maintained at the chosen temperature by controlling the sonic power input. The necessary input of sonic vibratory energy is controlled by instrumentation which senses the temperature at a given point, translates and feeds backthe appropriate signal to the transducer 1 to control the power, and thus maintains that temperature at a predetermined level. Such control enables the temperature of the material 2 to be elevated to and maintained at the hot working range at a chosen point preceding or adjacent to the area where the material 2 is worked by the rolls or even to permit the hot area to -be moved along the material 2. The use of this technique eliminates the need for the costly preheating operations and has the added advantage of providing an extremely accurate means of controlling the temperature of the material 2 as it enters the metal working tools 4.

In this invention a sonic power transducer 1, shown in FIG. 1, applies sonic vibratory power directly to nonresonant work material 2 to be hot rolled or deformed. The sonic power input is provided by high force piezoelectric or other electrical, mechanical, pneumatic, hydraulic, or other ultrasonic, or sonic generators 1 producing longitudinal wave outputs which are coupled to the Work material 2 (a) by threaded or other mechanical fasteners, (b) by intermediate impact tools, or (c) by other feasible coupling systems between the end 3 of the transducer 1 and the end of the work material 2. The sonic transducer 1 need not apply vibration to any part of the machinery such as the rolls 4 or other tools such as dies, presses, etc., used for applying static bias control forces used in the forming operation. This technique circumvents the basic difiiculties of attempting to vibrate large masses, and the chance of inducing fatigue failure into components of the machinery.

FIG. 2a shows the three modes of vibratory Waves which are utilized in the work material 2, selectively, to obtain multiple benefits in deforming and otherwise processing the work material. tReferring generally to FIG. 2a, Segment I, and FIG. 2b, Mode I is shown. Mode I permits the efficient transmission of sonic power in metals with maximum stress levels below the elastic limits 6, 7. The FIG. 2a shows a resulting stress wave 8 caused by the vibratory energy introduced by the aforementioned transducer 1. The solid portion of line 9 in FIG. 2b illustrates the maximum stress level attained by the illustrated vibratory stress 8 during Mode I transmission. The elastic range of the material is the linear region lying between positive elastic limit 6 and the negative elastic limit 7. So long as the stresses 8 introduced by the vibratory forces from the sonic transducer do not exceed the elastic limit 6, 7 of the material, the vibratory energy and resulting stress '8 are efficiently transmitted through the material.

Where the stress waves induced by the sonic transducer exceed the elastic limit 6, 7, the material is heated by 'Mode II, illustrated in FIG. 2a, Segment II, and FIG. 20. Mode II causes the heating of the work material 2 by the absorption of sonic power. That is, as illustrated in the Segment II of FIG. 2a, where the material 2 elastic limit 6, 7 is lower than the peak values of the vibratory stresses 8, the material is heated by mechanical hysteresis. FIG.

2c illustrates a typical hysteresis loop of the stress-strain curve caused by the fully reversed vibratory stress 8 exceeding the elastic limits 6 and 7. This illustrates the mechanism by which Mode II occurs when the elastic limits 6 and 7 are exceeded by the peak values of the sinusoidal vibratory stress 8. The amount of heat liberated by the sinusoidal stress 3 which exceeds both the positive and negative elastic limits of the material equals the integral of the hysteresis loop 11 (area contained within the mechanical hysteresis loop 11) in FIG. 20.

FIG. 3 illustrates how the elastic limit 6, 7 of a typical metallic material changes with increasing temperature. FIG. 3 is characteristic of carbon steel. Hence, mechanical hysteresis heating of the material may be induced by preheating the material to reduce its elastic limits. The change in the elastic limits of a material so heated is shown in FIG. 2a, Segment II. Heating the work material 2 to lower the elastic limit below the peak vibratory stress initiates the sonic heating which may then be used to maintain, increase or lower the temperature of the material 2 at a predetermined rate. The manipulation of the temperature is accomplished by controlling the sonic energy input. Also, by changing the sonic energy input, the heated zone may be caused to move. For example, increasing the sonic power input can move the heated zone toward the sonic transducer 1. This phenomenon enables the location of the heated zone of the work material 2 moving in direction 11 to be maintained at a predetermined position in advance of the forming machinery which may consist of rolls 4, dies, presses or other forming apparatus. That is, the heated zone can be caused to move in direction 17 at a rate equal to the movement of the material 2 in direction 11, thereby maintaining the heating zone a chosen distance from the point of entry of material 2 in forming device. The energy absorbed when the peak vibratory stress exceeds the elastic limits 6, 7 is shown by cross-hatched areas 10. As energy is absorbed by the work material 2 through mechanical hysteresis, the total energy transmitted through the work material 2 is diminished by an amount corresponding to that energy absorbed. As energy is absorbed the peak vibratory stress values become lower and the quantity of heat liberated through mechanical hysteresis is diminished in each subsequent cycle until the vibratory stress no longer exceeds the elastic limits of the work material 2. Referring to FIG. 1, Segment II, Mode II or sonic heating may also be initiated by reducing the cross-section of the metal. Reduction of the cross-section causes the sonic power input to exceed what the reduced cross-section can transmit without conversion into heat. The power is absorbed causing mechanical hysteresis and the ensuing heating of the material 2. As shown in Segment II of FIG. 1, Mode II is positioned at a chosen point while the material 2, moving in direction 11, enters the work rolls 4. Hence, when Mode III, deformation of metal by static bias force P or control-signal F is applied, the metal is at the desired hot working temperature and, therefore, the metal 2 is hot worked in this operation. Note, however, that the temperature, as discussed hereinbefore, may be maintained at any predetermined value.

The efficiency of sonic heating by Mode II is far greater than the conventional processes of induction and flame heating. The necessity of transporting the Work materials 2 from a preheat oven is eliminated. In fact, the preheat oven is unnecessary in the sonic heating process. Cooling of the work material 2 below the optimum working temperature before it reaches the forming devices is no problem because of the ease of maintaining the desired temperature at the desired location using sonic heating and the appropriate temperature sensing and feedback controls. Metals heated using sonic power are heated uniformly across the entire cross-section, eliminating thermal gradients and stresses characteristic in flame and induction heating processes due to nonuniform heating of the crosssection.

Vibratory energy not absorbed by the material 2 and not liberated in the form of heat continues to be transmitted through the material 2. When the material passes through the work rolls 4, dies or other forming apparatus and the static load F is applied by the rolls 4, dies or forming apparatus, the material 2 is deformed. The static force F is less by a factor of 10 to l00 than that required by conventional metal hot working processes. FIG. 4 is a graphical illustration of the mechanism by which the Mode III substitution of sonic vibratory force for static force occurs. The static force F applied to the rolls 4 in FIG. 1, Segment III is the bias force or control-signal necessary to utilize the vibratory energy re maining in and transmitted through the work material 2 after the Mode II heating by mechanical hysteresis.

The remaining dynamic stress 8 is equal to or very near to the elastic limit 6, 7 of the hot work material 2 (since no further conversion of sonic power into heat occurs within the elastic limits of the material 2). As in static hot forming, the elastic limit 6, 7 has been greatly reduced (e.g., from 40,000 p.s.i. to 4,000 p.s.i.) by the rise in material 2. temperature to the hot forging range. Hence, very little static force F is needed to cause the work material 2 stress peaks 8 to exceed the elastic limit 6, 7 causing an incremental deformation 13 to occur during each cycle of stress 8. Where the stress created by the static force F or control-signal is tensile (1 and the sum of the static tensile stress 0 and the dynamic stress 8 exceeds the elastic limit 6 of the material, incremental tensile deformation 13 ocurs as shown in FIG. 4.

The cross-hatched area 13 of FIG. 4 indicates the periods of time the work material 2 experiences total stress (dynamic stress 8 plus static stress in excess of its positive elastic limit 6 thereby causing the material 2 to deform. During each period in which the elastic limit 6, 7 is exceeded by the sum of the static bias stress UT and the dynamic stress 8, the work material 2 experiences an incremental deformation 13. Sonic vibratory stress added to a static bias stress causes small plastic deformation 15 or increments of movement along the plastic deformation portion 12 of the stress-strain curve, FIG. 2d. With vibratory frequencies such as 10 kHz., a small deformation is applied each cycle (every milliseconds). Each incremental deformation 13, 15 adds to produce the total permanent deformation or set 16. As the application of vibratory and static stressing continues, the work material follows the stress-strain curve, FIG. 2d, through its plastic deformation region 12 until the desired reduction in cross-section is achieved.

Where the static bias load causes a negative (compressive) static stress 0' to be introduced into the work material 2, the sum of this negative stress a and the dynamic stress 8 introduced by the transducer 1 will produce incremental compressive deformations 15 in a manner analogous to that described hereinabove in conjunction with the tensile stress 0-;- in FIG. 2d. The compressive stress 0 in FIG. 2d combines with the dynamic stress 8 to exceed the elastic limit 7 (in the negative or compressive direction) to produce incremental deformations. These incremental deformations occur in a manner analogous to the incremental deformation 13, 15 described for the tensile stress (I in FIG. 2d.

As the deformed work materials 2 pass beyond the forming rolls 4 or other deformation equipment, the transmitted sonic stress 8 is still sufiicient to provide stress relief effects in the hot material 2 as it starts to cool. The area in which this process occurs is illustrated by Segment IV of FIG. 1. This phenomenon offers advantages over certain present processes. Most present processes cause the work material 2 to be subject to thermal stress conditions during cooling that leads to undesirable stress distributions. Straightening or other final processing of bars, tubes, and other shapes is often required because of these locked-in stress conditions. Sonic stress relief effects occur with repeated reversed stressing, either above or below the elastic limit of the material. The stress relief etfect can also be of significant benefit after hot deformation operations.

Although certain and specific embodiments have been illustrated, it is to be understood that modifications may be made without departing from the true spirit and scope of the invention.

What is claimed is:

1. A process for the hot-forming of metal comprising the steps of applying vibratory-mechanical energy to the Work material thereby initiating mechanical hysteresis heating in said work material in a predetermined region, heating said predetermined region to a predetermined temperature controlling and maintaining said temperature of said work material in said predetermined region by modulation of said vibratory-mechanical energy, and applying static force to said work material at said heated predetermined region thereby deforming said work material.

2. A process as described in claim 1 wherein said process further comprises transmitting reversed dynamic stresses through said work material by applying said vibratory-mechanical energy to said work material.

3. A process as described in claim 2 wherein said process further comprises maintaining the amplitude of said reversed dynamic stresses at a value less than the elastic limit of said work material thereby permitting efficient transmission of said reversed dynamic stresses to said predetermined region where said mechanical hysteresis heating is effected by absorption of a portion of the energy in said reversed dynamic stresses.

4. A process as described in claim 3 wherein said process further comprises lowering the elastic limit of said work material in a predetermined region in advance of said static force by raising the temperature of said predetermined region of said work material to said predetermined temperature.

5. A process as described in claim 4 wherein said step of initiating mechanical hysteresis heating in said work material in said predetermined region further comprises applying a gas flame to said predetermined region of said Work material wherein said temperature of said work material in said predetermined region is raised thereby lowering said elastic limit of said work material.

6. A process as described in claim 5 wherein said process further comprises liberating heat by mechanical hysteresis as the amplitude of said reversed dynamic stresses exceeds said elastic limits in said predetermined region.

7. A process as described in claim 4 wherein said step of initiating mechanical hysteresis in said work material in said predetermined region further comprises heating said predetermined region of said work material using induction heating means wherein said temperature of said work material in said predetermined region is raised thereby lowering said elastic limit of said work material.

8. A process as described in claim 7 wherein said process further comprises liberating heat by mechanical hysteresis as the amplitude of said reversed dynamic stresses exceeds said elastic limits in said predetermined region.

9. A process as described in claim 1 wherein said step of initiating mechanical hysteresis heating in said work material in said predetermined region further comprises reducing the cross-section of the work material in said predetermined region.

10. A process as described in claim 9 wherein said process further comprises liberating heat by mechanical hysteresis wherein the vibratory-mechanical energy input exceeds what the reduced cross-section can efficiently transmit, said vibratory-mechanical energy thereby creating peak vibratory stress levels exceeding the elastic limits of said work material.

11. A process as described n claim 6 wherein the con- 8 trolling of said predetermined temperature of said predetermined region further comprises the steps of modulating the input of said vibratory-mechanical energy thereby controlling the amplitude of said reversed dynamic stresses thereby controlling said heat released by mechanical hysteresis.

12. A process as described in claim 8 wherein the controlling of said predetermined temperature of said predetermined region further comprises the steps of mod .ulating the input of said vibratory-mechanical energy thereby controlling the amplitude of said reversed dynamic stresses thereby controlling said heat released by mechanical hysteresis.

13. A process as described in claim 10 wherein the controlling of said predetermined temperature of said predetermined region further comprises the steps of modulating the input of said vibratory-mechanical energy thereby controlling the amplitude of said reversed dynamic stresses thereby controlling said heat released by mechanical hysteresis.

14. A process as described in claim 13 wherein said process further comprises transmitting beyond the heated region said vibratory-mechanical energy not liberated as heat by said mechanical hysteresis.

15. A process as described in claim 1 wherein said process further comprises deforming said work material as said static forces are applied to said predetermined region at said predetermined temperature.

16. A process as described in claim 15 wherein said process further comprises stress-relieving said hot-formed work material by reversed dynamic stresses created by said vibratory-mechanical energy remaining in said hotformed work material after said work material has been hot-formed by said combination of dynamic and static stresses.

17 A combination for the hot-forming of metal comprising: means for applying static forces to deform the work material, means for supporting and guiding said work material through said deforming forces, means for applying heat to said work material at a predetermined region correlated with the movement of said work material, a source of electromechanical energy, and means for coupling said source of electromechanical energy to one end of said work material.

18. A combination as set forth in claim 17 wherein said means for applying heat to said work material is a gas flame.

19. A combination as set forth in claim 17 wherein said means for applying heat to said work material is induction heating means.

20. A combination as set forth in claim 17 wherein said source of electromechanical energy is a high-power electromechanical sonic transducer.

21. A combination as set forth in claim 17 wherein said electromechanical energy further includes as electromechanical transducer and wherein said means for References Cited UNITED STATES PATENTS 8/1965 Allison 2l97.5 11/1967 Bodine 72297 LOWELL A. LARSON, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 S34 574 Dated October 20 1970 Robert C. McMaster Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 45, "milliseconds" should read microseconds Signed and sealed this 25th day of May 1971.

(SEAL) Attest: E

EDWARD M. FLETCHER,JR. WILLIAM E SCHUYLER JR. Commissioner of Patents 1 Attesting Officer 

